Sarcoidosis is an inflammatory disease of unknown etiology that occurs worldwide and is characterized by granuloma formation in different organs. No specific test has been developed to diagnose this disease. Confirmation of non-caseating granuloma in tissue biopsy of involved organs in the absence of other causes is the current state of the art for diagnosing sarcoidosis. We propose to test the hypothesis that overall immunity plays a prominent role in the pathogenesis of sarcoidosis, since abnormalities of the immune function and the presence of various antibodies/autoantibodies occurs in this disorder. Sarcoidosis and tuberculosis have clinical and pathological similarities. Despite isolation of various components of Mycobacterium tuberculosis (MTB) from sarcoidosis tissues, sarcoidosis subjects react to tuberculin skin test (PPD) negatively. In contrast to sarcoidosis latently infected individuals with TB (LTBI) respond to PPD with delayed type hypersensitivity reaction. Using a high throughput method, we developed a complex cDNA library derived from tissues of sarcoidosis patients. We constructed a microarray platform from this cDNA library containing large numbers of sarcoidosis clones and immunoscreened this platform with sera from patients with sarcoidosis, controls and other respiratory diseases. We identified a panel of biomarkers/classifiers with high sensitivity and specificity that can discriminate between sera of patients with sarcoidosis, healthy controls other respiratory diseases. Thus, our technology allows us to test the hypothesis that sarcoidosis is an immune disorder triggered by a group of specific antigens, which differ from LTBI antigens. Furthermore, these specific antigen peptides are capable of inducing granuloma in vitro in sarcoidosis peripheral mononuclear cells (PBMCs). To test this hypothesis, we will selectively biopan our T7 phage cDNA display library with sera of diverse sarcoidosis and LTBI subjects to select diversified clones to increase the antigen repertoire to construct a comprehensive antigen microarray platform. Second, we propose to use a large sample size from a diversified population of sarcoidosis patients and healthy controls as well as subjects with LTBI. We would like to expand test the bioreactivity of sera obtained independently from cases and controls to identify a panel of diagnostic biomarkers/classifiers, which can discriminate between sarcoidosis and healthy controls and latent TB. Furthermore, we will validate the classifiers in independent validation sets and determine whether the discovered biomarkers/classifiers can determine the clinical outcome, especially in the progressive disease course. In Aim 3, we will synthesize the antigen peptides to develop an ELISA to determine the titers of identified antigens. Finally, we test whether these clones are capable of generating granuloma in vitro using latent, healthy controls and sarcoidosis peripheral mononuclear cells. The overall goal is to define the specific antigens initiating granuloma formation in sarcoidosis and how the immunological response to antigen leads to sarcoidosis and latent TB phenotypes.